Monochromatic light
of wavelength λ is shone on a photoelectric tube (metal cathode in a vacuum tube) as shown in the figure at the right. The metal in the cathode has a workfunction with a value of φ.
As set up, the light fails to produce any photoelectrons, even when there
is no retarding voltage placed on the tube. In order to try to get photoelectrons
out, it would be appropriate to try the following: (Give all answers that
are correct.)